Wallace, a two-time winner this year driving the No. 54 Toyota, turned a fast lap of 125.264 mph on the .533-mile track. He was just ahead of teammate and team owner Kyle Busch, who clocked a lap at 124.930 mph in the KBM No. 51 Toyota.

Busch, the defending race winner with four career Bristol victories in the series, will be going for a tripleheader sweep in all three NASCAR national series this week at Bristol.

NASCAR Next driver Gray Gaulding, 16, was third-fastest in the NTS Motorsports No. 20 Chevrolet at 123.970 mph. He will be making only his fifth career start in the series in Wednesday night's UNOH 200 Presented by ZLOOP (8:30 p.m. ET, FOX Sports 1).

Four-time series champion Ron Hornaday Jr. was fourth-fastest in practice with 16-year-old Cole Custer, the pole winner earlier this season at Gateway Motorsports Park, completing the top five in practice.

NASCAR K&N Pro Series East points leader Ben Rhodes, 17, was eighth-fastest in preparation for just the third series start of his career.

Morning rain had pushed back the opening schedule a half-hour from its originally scheduled 10 a.m. ET start. Precipitation held off long enough for the combined NASCAR Whelen Modified and Southern Modified tours to get in their opening practice, but a drizzle placed the schedule on hold.

After some eventual clearing, the NASCAR Air Titan system worked to quickly dry the concrete surface. NASCAR officials altered the race-day schedule to combine the two shorter practices into a single session -- from 11:45 a.m. ET (when the track was deemed race-ready) to 1:30 p.m. ET.

Keystone Light Pole Qualifying for the 13th of 22 races this season is scheduled for 4:40 p.m. ET (FS1).

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